Reduction of Axial Turbomachinery Tonal Noise by Means of Flow Induced Secondary Sources Using an Extremum-Seeking Control Technique

Abstract

In conventional active noise control experiments, loudspeakers are used to generate the secondary anti-phase sound field to be superimposed destructively with the sound waves radiated from the primary source. In the present study, aerodynamic sound sources are used to actively control the tonal noise of an axial fan. This is achieved by disturbing the flow field around the blade tips in such a way that additional periodic forces are set up which in turn form the secondary sound sources. To disturb the flow, air is blown into the blade tip region through the casing wall. The resulting aerodynamic sound sources are adjustable in both amplitude and phase. Results for closed loop control of the blade passing frequency using an extremum-seeking control technique are presented.